Ceramic material based on bismuth niobate substituted with zinc

ABSTRACT

The invention relates to ceramic materials based on bismuth niobate substituted with zinc and can be used for producing multilayer high frequency thermostable ceramic condensers provided with electrodes based on an alloy which comprises Ag and Pd, and also for producing multilayer microwave films. The aim of the invention is to develop a ceramic material having a low sintering temperature sufficient for using silver-palladium electrodes having a silver content of up to 90%. Said material has an optimum dielectric permittivity and thermostability which are sufficient for producing a wide range of items based on said material. Zinc niobate ZnNb2O6 having a structure of columbite with a quantity ranging from 7.0 to 99.0, expressed in mass %, is added into a ceramic material based on the bismuth niobate substituted with zinc having a crystal-chemical formula (Bi⅔[ ]⅓)2(Zn&lt;2+&gt;⅓Nd⅔)2O6[ ]1,[ ] being a vacancy with a pyrochlore structure. Glass having the following component ratio, in mass %, can be added into the material: PbO ranging from 26 to 33, Bi2 ranging from 14 to 24, B2O3 ranging from 4 to 10, TiO2 ranging from 15 to 21, ZnO ranging from 21 to 28.

FIELD OF THE INVENTION

The invention relates to ceramic materials based on bismuth niobate substituted with zinc and can be used for producing multilayer high frequency thermostable ceramic condensers provided with electrodes based on an alloy which comprises Ag and Pd, and also for producing multilayer microwave filters.

BACKGROUND OF THE INVENTION

In production of condensers high frequency ceramic materials with sintering temperature not in excess of 1120° C. are applied, which makes it possible to use an Ag—Pd alloy, containing no more than 30% of Pd as inner electrodes of monolithic condensers. A set of modern requirements to radio electronic equipment makes high demands of such characteristics of ceramic materials as dielectric permeability which must provide the production of the whole range of rated values of ceramic condensers, including the low capacitance range which is possible only when the level of dielectric permeability does not exceed 40, the temperature coefficient of dielectric permeability and the tangent of the angle of dielectric losses (tg δ) or the factor of merit (Q˜1/tg δ). The latter parameter is especially important for microwave filters.

A ceramic material for high frequency condensers is known with a temperature coefficient of capacitance within the range from −30·10⁻⁶deg.⁻¹ to +30·10⁻⁶deg.⁻¹, which contains a solid solution with formula (Ba_(0.9) Sr_(0.1)) (Nd_(0.8) Bi_(0.2))₂·Ti₄ O₁₂ and glass forming compound of borosilicate xB₂O₃·ySiO₂ used as an additive (see patent RU N 2035778, H 01 G 4/12).

Disadvantages of this material are high dielectric permeability which makes it impossible to produce on its base low capacitance multilayer ceramic condensers (several picofarads) and not low enough sintering temperature which prevents from using alloys with Pd content below 30% as electrodes for muitilayer condensers and filters.

Bismuth niobate substituted with magnesium, zinc and nickel are known with crystal chemical formula (Bi_(2/3)[ ]_(1/3))₂(Zn²⁺ _(1/3)Nd_(2/3)) ₂O₆)[ ]₁, where [ ] —a vacancy as high frequency condenser materials with high dielectric permeability (∈=145-148) at a temperature coefficient of dielectric permeability corresponding to groups M330 and M470 of thermostability and a low value of tangent of the angle of dielectric losses tg δ=(2-3)·10⁻⁴ (see patent RU N 2021207, C 01 G 33/00).

This technical solution is selected as a prototype of this invention.

Disadvantages of the prototype that make it impossible to solve our problem is relatively high sintering temperature which makes it necessary to use more expensive electrodes and low thermostability which prevents production of thermostable ceramic condensers and microwave filters on the base of this material.

DISCLOSURE OF THE INVENTION

The aim of the invention is to develop a ceramic material having a low sintering temperature sufficient for using silver-palladium electrodes having a silver content of up to 90%. The said material has an optimum dielectric permittivity and thermostability which are sufficient for producing a wide range of items based on said material.

According to the invention ceramic material based on bismuth niobate substituted with zinc having a crystal-chemical formula (Bi_(2/3)[ ]_(1/3))₂(Zn²⁺ _(1/3)Nb_(2/3))₂O₆[ ]₁ with a pyrochlore structure is characterized that zinc niobate ZnNb₂O₆ having a structure of columbite with a quantity ranging from 7.0 to 99.0, expressed in mass % is added to the said material. Glass having the following component ratio, in mass %, can be added into the material: PbO ranging from 26 to 33, Bi₂O₃ ranging from 14 to 24, B₂O₃- 4-10, TiO₂ ranging from 15 to 21, ZnO ranging from 21 to 28 in the amount of 0.1-5.0 mass %.

The Applicant did not find any sources that contain the information on similar technical solutions, which allows, in the Applicant's opinion, to make a conclusion that the invention meets the “Novelty” criterion (N).

By implementation of the distinguishing features of the invention (in combination with the features indicated in the restrictive part of formula of invention) new important properties of the subject are reached. In the technical solution proposed high values of all basic technical characteristics that determine the fitness of the material for using it in production of multi-layer high frequency condensers and filters are reached, that is sintering temperature, optimal permittivity and high thermostability.

The Applicant did not find any information on the influence of the distinguishing features of the invention on the technical result obtained. This allows to make a conclusion that the technical solution applied conforms to the “Invention standard” criterion (IS).

BRIEF DESCRIPTION OF DRAWINGS

Further the invention is explained by detailed description of examples of its implementation without any references to drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technique of producing the compound proposed is as follows. First niobate substituted with zinc with a pyrochlore structure is synthesized, next zinc niobate with a structure of columbite is synthesized. The components thus obtained are mixed and wet grinded glass is added, next it is dried and the invented material is obtained.

For the examples of synthesis of the invented compound see table 1.

For main technical characteristic of specimens of the materials obtained see table 2.

The analysis of the results shows that wide application of zinc niobate makes it possible to expand the series of new materials in a wide range of thermostable, and thermocompensating groups, ensures the possibility to produce a wide range of ceramic condensers, including the condensers belonging to the most advanced MO group with electrodes containing not less than 30% of Pd and ensures the production of low capacitance thermostable ceramic condensers and thermostable microwave filters.

Specimens 1 through 8 correspond to thermostability groups 100, 33, MO, M47 and M75, specimens 9 through 11- to thermocompensating groups M150, M220 and M330 in accordance to OST 110309-86 “Ceramic materials for development of electronic equipment. Specifications.”.

Addition of glass of the said composition (RU, C1, 2035780) into the invented material ensures additional reduction of sintering temperature its range being widened, results in some decrease of thermostable and thermocompensating properties (in terms of the absolute value) and dielectric losses, improves technological properties of the material which is very important in production of multiplayer condensers and filters.

INDUSTRIAL APPLICABILITY

The proposed material can be obtained by industrial method with application of widespread materials, known techniques and technical aids which stipulates in the Author's opinion the conformity of the invention to the “Industrial applicability” criterion (IA).

TABLE 1 Chemical composition, weight, % Bismuth niobate Zinc niobate Specimen No substituted with zinc ZnNb₂O₆ Glass 1 1.0 99.0 0.2 2 10.0 90.0 0.1 3 15.0 85.0 — 4 15.0 85.0 2.0 5 17.5 82.5 5.0 6 20.0 80.0 1.0 7 26.0 74.0 3.0 8 37.5 62.5 0.5 9 50.0 50.0 0.2 10 62.5 37.5 2.0 11 93.0 7.0 4.0

TABLE 2 Temperature coefficient of Sintering Tangent of angle of dielectric temperature dielectric losses, Specimen Dielectric permeability, (Tsn), tgδ × 10⁴ at f = 1 MHz No permeability TCE · 10⁰ deg⁻¹ ° C. 25° C. 125° C. 1 22 . . . 23 +118 . . . +135 1040 . . . 1060 0.2 . . . 1.5 0.4 . . . 3.0 2 27 . . . 29 +74 . . . +86 1020 . . . 1060 0.5 . . . 1.0 0.8 . . . 1.6 3 30 . . . 32 +44 . . . +50 1000 . . . 1060 0.6 . . . 1.2 0.8 . . . 1.6 4 29 . . . 31 +32 . . . +38  980 . . . 1040 0.4 . . . 0.7 0.6 . . . 1.0 5 31 . . . 33 −12 . . . +7   960 . . . 1060 0.2 . . . 0.4 0.3 . . . 0.8 6 32 . . . 34  0 . . . +10  980 . . . 1040 0.4 . . . 0.6 0.5 . . . 0.8 7 35 . . . 37 −22 . . . −24  960 . . . 1060 0.1 . . . 0.5 0.2 . . . 1.0 8 41 . . . 43 −73 . . . −80 1020 . . . 1060 0.5 . . . 0.1 0.9 . . . 1.7 9 81 . . . 84 −144 . . . −162 1020 . . . 1060 1.2 . . . 1.5 1.2 . . . 2.0 10  98 . . . 101 −215 . . . −240  980 . . . 1060 1.1 . . . 1.5 2.0 . . . 2.5 11 132 . . . 140 −315 . . . −350  980 . . . 1040 0.6 . . . 2.0 2.0 . . . 3.0 

1. Ceramic material based on bismuth niobate substituted with zinc having a crystal-chemical formula (Bi_(2/3)[ ]_(1/3))₂(Zn²⁺ _(1/3)Nb_(2/3))₂O₆[ ]₁ with a pyrochlore structure is characterized that zinc niobate ZnNb₂O₆ having a structure of columbite with a quantity ranging from 7.0 to 99.0, expressed in mass % is added to the said material wherein [ ] is a normally occupied lattice site from which an atom or ion is missing.
 2. The Ceramic material of claim 1, characterized that glass having the following component ratio, in mass %, is added into the material: PbO ranging from 26 to 33, Bi₂O₃ ranging from 14 to 24 B₂O₃ ranging from 4 to 10, Ti0₂ ranging from 15 to 21, ZnO ranging from 21 to 28 in the amount of 0.1-5.0 mass %. 